Saturday, April 25, 2015

Tonight's Sky for April 25: Astronomy Day/First Quarter Moon

Today
marks a little known holiday: International Astronomy Day, which
began as a 1-club event and eventually spread to encompass the entire
world. With
humble origins as an attempt at public outreach by the Astronomical
Association of Southern California, the effort to bring astronomy to
the masses, often city dwellers, quickly grew in popularity to the
point where the holiday eventually went national, and then
international. Now, over 40 years after the first Astronomy Day
(1973) the holiday continues to grow and become more relevant.

Why the part about being relevant? Simple: dark skies are going away
fast.

When the first Astronomy Day was launched in 1973, the whole idea was
to set up telescopes in public places where astronomers could show
members of the general public the wonders of the universe. Naturally,
to guarantee that the public would show up, the telescopes had to be
set up in urban/suburban locations, areas that are not all that good
for astronomy. Obviously, by looking at the success of the holiday,
people are seeing things in the telescopes.

Lesson of the day:
you can do astronomy from just about anywhere.

For starters, Astronomy Day is always coordinated to coincide as best
possible with First Quarter Moon
as it is always visible as it is the second brightest thing in the
sky after the Sun. Believe it or not, there are astronomers who spend
the majority of their telescope time studying the Moon. Second,
planets. All of the planets are generally of 0 magnitude or brighter,
thus visible from all but the most light polluted areas. Being bright
targets, the planets are also good targets for examination by
city-dwellers. For suburbanites, binary (double, triple, etc.) stars
are also a lot of fun to look at because they, too, can be observed
in all but the worst of lighting conditions.

So
yes, the dark skies are going away more every year but, if you know
what to look for and are content with the fact that you may not be
able to see deep sky nebulae, galaxies, and clusters from your
backyard, there is plenty of fun to be had with a telescope in a
city.

On top of the festivities, the
Moon,
second brightest object in the sky, has reached the First Quarter
phase, which means that it is exactly 90 degrees around its orbit of
Earth and is one quarter finished with its current orbit..

As
for lunar mechanics, the Moon is always half lit. The reason we don't
always see it as such is thanks to orientation in relation to us.
Right now, with the Moon at a 90 degree angle relative to the
Earth-Sun line, we only see half of the lit side.

After
today, we will see more of the Moon each night as its lit side turns
more toward from us and heads toward Full in a week.